Recently, new ionic liquid alkylation processes have been disclosed for the production of alkylates, in particular fuel-blending components like trimethylpentanes (TMPs), which have research octane numbers (RONs) of greater than 100. In such processes isoparaffins are alkylated with olefins using an acidic ionic liquid catalyst.
For instance, U.S. Pat. No. 7,285,698 discloses a process in which a composite ionic liquid catalyst is used to react isobutane with a butane under alkylation conditions. The reactor effluent is separated and the ionic liquid phase is recycled to the reactor while the hydrocarbon phase is treated to retrieve the alkylate. It has however been found that during operation of such an ionic liquid alkylation process, solids are formed. As the reaction progresses, these solids accumulate in the reaction zone and may lead to blockage of pathways and/or valves. In WO2011/015639 a process is described for removal of the solids formed during the ionic liquid alkylation process.
It is important to maintain the solids content in the ionic alkylation process at pre-defined levels thereby minimizing the need for addition of fresh ionic liquid catalyst.